Cooling lubricant emulsion

ABSTRACT

A process for preparing a stable cooling lubricant emulsion for use in the cutting of metals involves the steps of (a) forming a mixture having an oil component, water and an emulsifier with the oil component being emulsified in the water, then (b) dispersing into 100 parts by weight of the mixture by means of high shear from about 1 to about 14 parts by weight of a natural, water-immiscible cutting oil. The stable oil-in-water cooling lubricant emulsion formed has at least 50 percent of the cutting oil present in the form of particles having a diameter of 0.5 to 8 μm. The cooling lubricant emulsion formed may be used in an extended range of applications.

BACKGROUND OF THE INVENTION

This application is filed under 35 U.S.C. § 371 and based onPCT/EP98/00277, filed Jan. 20, 1998, now WO 98/32818.

1. Field of the Invention

This invention relates to a new type of cooling lubricant emulsion forthe cutting of metals and to a process for the preparation of such anemulsion.

2. Discussion of Related Art

Cooling lubricants are preparations/mixtures which are used for coolingand lubricating the tools during metal cutting and metal forming. Themost important processing operations are differentiated by the type ofmovements made by the processed part and the tool, by the geometry ofthe parts being produced and the processing conditions. Onedistinguishes, for example, milling, turning, drilling and grinding asbeing cutting processes, and rolling, deep drawing and cold extrusion asbeing deformations without cutting.

The common principle of the metal-cutting processes is that the cuttingedge of the tool cuts into the material and in doing so removes asplinter from the surface, so that a new surface is formed. Very highpressures are required for cutting into the material. The deformation ofthe splinter and the friction produced under the pressure produce heat,which heats the workpiece, the tool and, above all, the splinters.

The required effect of using cooling lubricants is therefore thelowering of the temperature, which otherwise may rise, for example, upto 1000° C. in the splinters and which affects the dimensional accuracyof the parts produced. Another major task of the cooling lubricant is toextend the useful life of the tools, which wear rapidly under theinfluence of elevated temperatures. The roughness of the surfaces isdecreased by the use of a cooling lubricant, as the lubricant preventswelding of the tool and the surface of the workpiece and avoids adhesionof particles. Moreover, the cooling lubricant assumes the task oftransporting away the splinters formed.

A clear definition of cooling lubricants has been established in therevised version of DIN 51385 No. 1, the items in question being coolinglubricants which are immiscible with water, water-miscible and mixedwith water. According to DIN 51385, the term “mixed with water” refersto the fmal condition of the prepared medium (in most cases oil-in-wateremulsions), but “water-miscible” refers to the condition of theconcentrate.

Cooling lubricants mixed with water are prepared on the user's premisesby mixing together a concentrate of the water-miscible cooling lubricantand tap water. Generally ca. 5% aqueous emulsions are prepared. Theadvantage of this type of cooling lubricant is the good cooling action,which is due to the thermal properties of the water. As a result of thegood cooling action, it is possible to achieve very high operatingspeeds and thereby to increase the productivity of the machines. Thelubricating action of the cooling lubricants mixed with water isadequate for most processing methods involving cutting. A furtheradvantage lies in the low costs, which are achieved owing to thefeasibility of mixing the concentrate with water. A disadvantage ofcooling lubricants mixed with water is that they are susceptible toexternal influences, in particular to attack by microorganisms, andtherefore require more control and care than do cooling lubricants whichare immiscible with water, such as cutting oils, grinding oils andforming oils.

The Table below provides a summary of the requirements for coolinglubricants which are water-miscible and for those which are mixed withwater:

cooling and lubricating action

rust protection

no attack on non-ferrous metals

toxicological safety, in particular skin tolerance

no foam formation

no attack on paints and seals

emulsion stability

no agglutination or resinification

good miscibility

pleasant aroma

clean appearance

good filterability

trouble-free disposal.

A survey of the processes for forming metals and of the auxiliariesconventionally used for this purpose may be found, for example, inUllmann's Encyclopaedia of Industrial Chemistry, 5th Ed., Vol. A15,479-486. The range of the available forms of the suitable auxiliariesextends from oils, via oil-in-water emulsions, to aqueous solutions.

Cooling lubricants which are immiscible with water and those which arewater-miscible are frequently based on mineral oil. The grades ofmineral oils used are predominantly combinations of paraffinic,naphthenic and aromatic hydrocarbon compounds. Besides the mineral oils,so-called synthetic lubricants (“synthetic oils”), such as polyalphaolefins, polyalkylene glycols and polyalkylene glycol ethers, dialkylethers, acetals, natural ester lubricants, as well as synthetic estersand derivatives thereof are also important.

To be capable of fulfilling the requirements in practice, coolinglubricants must contain various components in addition to the oil base.The most important groups of substances are the emulsifiers,anti-corrosion additives, biocides, EP additives, polar additives,antifogging additives, antioxidants, solid lubricating additives anddefoaming agents.

Emulsifiers (for example, surfactants, petroleum sulfonates, alkalisoaps, alkanolamine soaps) stabilise the fine distribution of oildroplets within the aqueous operating liquid, which is an oil-in-wateremulsion. The emulsifiers are quantitatively an important group ofadditives for the water-miscible cooling lubricants.

Conventional anti-corrosion additives (for example, alkanolamines andsalts thereof, sulfonates, organic boron compounds, fatty acid amides,aminodicarboxylic acids, phosphate esters, thiophosphonic esters,dialkyldithiophosphates, monoalkylaryl sulfonates and dialkylarylsulfonates, benzotriazoles, polyisobutene succinic acid derivatives) areintended to prevent the rusting of metal surfaces. Some anti-corrosionadditives simultaneously have emulsifying properties and are thereforealso used as emulsifiers. Biocides (for example, phenol derivatives,formaldehyde derivatives, “Kathon MW”) are intended to inhibit thegrowth of bacteria and fungi. EP additives (for example, sulfurised fatsand oils, phosphorus-containing compounds, organochloro compounds) areintended to prevent microwelding between metal surfaces at highpressures and elevated temperatures. Polar additives (for example,natural fats and oils, synthetic esters) increase the lubricatingproperties.

Antioxidants (for example, organic sulfides, zinc dithiophosphates,aromatic amines) ensure that the cooling lubricants have a long-potlife.

In addition to the cooling action, the second important function ofcooling lubricants is the lubricating action (see the article by W.Klose: “Kühlschmiermittel auf Metalloberflächen”, Mitteilungen desVereins Deutscher Emailfachleute, 41, Number 11, pages 138-142 (1993)).According to this, the action of the lubricating components depends onthe formation of surface layers which possess a lower shear strengththan that of the underlying material and therefore reduce friction andwear. The range of surface conditions extends from adsorptively bondedlayers, via chemisorption, to chemically reactive layers, which producea strong bond to the metal surface.

Adsorptive lubricating films are the simplest form of lubricatingcovering on a surface. They are produced, for example, by mineral oilswithout specialised additives. The formation of the adsorbed layers maybe promoted by additions of polar active substances, such as fattyalcohols or fatty esters. Here, over and above the purely physicaladsorption, there occurs an interaction between the metal surface andthe molecules of the lubricant, which results in a partial chemisorptivebonding of the fatty alcohol or of the fatty ester.

Fatty acids are typical examples of chemisorptive lubricating layerformers. The hydrophilic carboxyl group is chemically bonded to themetal surface by reaction with the metal atoms and the hydrophobichydrocarbon group is aligned vertically to the surface. The increasedadhesive strength of the chemisorptive layer improves the capacity toabsorb pressure compared with that of purely adsorptive lubricatingfilms, but, in many cases of metal forming, is still not sufficient toreduce friction and wear. Here only admixtures of EP or AW additives(extreme pressure or antiwear additives) bring about an adequateimprovement in the lubricating performance, so that even complex formingprocesses are rendered possible. These additives are generally activesubstances containing chlorine, phosphorus or sulfur. The action thereofdepends on the development of chemically reactive layers in the form ofmetal chlorides, metal phosphates or metal sulfides. For reasons ofdisposal, nowadays endeavours are made to dispense withchlorine-containing EP additives if possible. The reactive layers formedat the metal surface act, on the one hand, as solid lubricating films,which are constantly worn away and renewed during the forming process.On the other hand, they form monomolecular surface films, which may takeup additional lubricating components.

Cooling lubricants mixed with water are a common type of coolinglubricant. In practice, however, different cooling lubricants mixed withwater are used in order to satisfy the different requirements withregard to corrosion protection of the various materials processed,lubricating action at high operating speed, pot-life and, not least,industrial safety provisions and environmental requirements. Manydifferent types of cooling lubricant concentrates have therefore to beproduced, stored and transported in small batches by the manufacturersof these substances. At the user's premises, emulsions which are stillusable may have to be discarded, if another type of cooling lubricantbecomes necessary because of a change in materials. These processes arecost-intensive and disadvantageous from the environmental aspect.

There is accordingly a need for a new cooling lubricant emulsion of thetype mixed with water, which may be used for an extended range ofapplications. Such a new type of cooling lubricant is made availablethrough the finding that it is possible, by the application of highshear energy, to emulsify a natural cutting oil which is immiscible withwater in a conventional per se cooling lubricant emulsion mixed withwater, and thereby to obtain a stable oil-in-water emulsion. Such acombination of at least two oil components may be used for a wide rangeof applications.

DESCRIPTION OF THE INVENTION

One embodiment of the present invention accordingly relates to a processfor the preparation of a cooling lubricant emulsion for the cutting ofmetals, wherein:

(a) from 2 to 15 parts, by weight, of a water-miscible concentrate of acooling lubricant emulsion is mixed with from 98 to 85 parts, by weight,of water, in order to obtain a mixture containing 100 parts, by weight;and, subsequently,

(b) from 1 to 14 parts, by weight, of a natural cutting oil which isimmiscible with water is dispersed in the mixture (a) by means of strongshearing.

Here it is preferable to use fewer parts, by weight, of cutting oilimmiscible with water than parts, by weight, of water-miscibleconcentrate. The proportions of cutting oil to the proportions ofwater-miscible concentrate are preferably, for example, between 10 and80 to 100 and in particular, for example, between 20 and 70 to 100.

Therefore, the present invention mainly involves, contrary to the usualinstructions in practice, the dispersion of a natural cutting oil whichis per se immiscible with water in a conventional per se coolinglubricant emulsion. For this a shear energy is required which is highcompared with the prior art for preparing cooling lubricant emulsionsmixed with water. The required shearing may be produced, for example, bystirring with a toothed disc. Alternatively, intensive mixers, such asan Ultraturrax (rate of rotation 10,000 to 20,000 revolutions perminute) or high-rotating rotor-stator systems are suitable. Where anUltraturrax is used, dispersion is achieved by 20,000 revolutions perminute for a period of from about 1 to about 5 minutes. An alternativeto this, available during the operation, involves introducing thecutting oil into the operating system at a point where turbulence ishigh. The dispersion then takes place as a result of the shear forcesduring the metal processing operations.

The individual components here are well-known as cooling lubricants oras concentrates for cooling lubricant emulsions in prior art. Forexample, in step (a) one may use an emulsion concentrate which consistsof about 20 to about 60 wt. % of an oil component, preferably esterlubricant, but also contains paraffinic or naphthenic mineral oil, whichmay if desired contain lubricating additives, and from 0 to 25 wt. % ofwater. The remainder, bringing the total to 100 wt. %, comprisesemulsifiers, preferably based on fatty alcohol ethoxylates, corrosioninhibitors, preferably based on alkali metal carboxylates, amine soaps,ethanolamine soaps and/or ethanolamides, and optionally other auxiliaryand active substances known in the prior art for this group of products,for instance, those listed in the concentrates given as Examples.

Synthetic oils, for example polyolefms, may be used instead of themineral oil. Acetals or dialkyl ethers are alternative oil componentshaving increased biodegradability.

For example, the concentrate used in step (a) may be a water-misciblecooling lubricant emulsion consisting of (data in wt. %):

Concentrate 1 57% mineral oil 16.5% C₁₄-C₂₀ fatty acid mixture 4.4%potassium hydroxide solution, 45% 5.5% alkylsulfonamide carboxylic acid7.0% hexanediol 4.0% petroleum sulfonate 0.4% triazole derivative 3.0%hexahydrazine derivative 0.2% o-phenylphenol Remainder: demineralisedwater

Concentrate 2 35% mineral oil 7.5% C₁₄-C₂₀ fatty acid mixture 11.5%C₃₂-C₃₆ dimeric fatty acid mixture 8.0% C₆-C₉ carboxylic acid mixture12.5% potassium hydroxide solution, 45% 17.0% ethoxylated fatty alcohol(2 to 5 ethylene oxide groups) 3.0% hemiacetal 0.3% Na pyrion Remainder:demineralised water

Concentrate 3 35.5% mineral oil 6.5% C₁₄-C₂₀ fatty acid mixture 7.0%boric acid 3.0% C₆-C₉ carboxylic acid mixture 11.0% mixture of primaryand tertiary alkanolamines 8.5% fatty acid amide 8.5% ethoxylated fattyalcohol (2 to 5 ethylene oxide groups) 1.0% butyl diglycol 0.2% Napyrion Remainder: demineralised water

In step (b), ester-based oils are used as cutting oils immiscible inwater. Examples of these are natural triglycerides or modificationproducts thereof, waxy esters and fatty acid esters of monoalkanolshaving 4 to 12 carbon atoms, for example, the ethylhexyl ester of tallowfatty acid, or transesterified rape-seed oil, as well as fatty acidesters of polyols, wherein trimethylolpropane in particular may be usedas polyol component. Mixtures of these oils may also be used in step(b). The oils may contain additional auxiliary substances; examples ofthese which may be particularly mentioned are EP additives, for example,in the form of sulfurised compounds, antioxidants and corrosioninhibitors. The cutting oil which is immiscible in water is preferablyselected from oxidation-stabilised fatty acid glycerides in the form oftriesters containing three fatty acids having 14 to 22 carbon atoms perfatty acid molecule and oxidation-stabilised diesters containing twofatty acids having 12 to 22 carbon atoms per fatty acid molecule.

Another embodiment of the present invention relates to a ready-to-usecooling lubricant emulsion mixed with water, of the oil-in-water type,which may be prepared directly at the user's premises by means of theprocess described above. The emulsion could also be prepared centrallyand be transported to the individual users. This is uneconomic anddisadvantageous environmentally, as it would necessarily involve thetransport of large quantities of water.

For the preparation of the emulsion according to the present invention,it is not necessary to carry out the steps (a) and (b) in immediatesuccession. Rather, a user of a conventional cooling lubricant emulsionmay also carry out part (b) of the present invention by subsequentlydispersing, in the manner described in more detail above, a cutting oilin this emulsion after it has already been put into use.

The present invention also relates to the use of the present coolinglubricant emulsion for the cutting of metals. Examples of such cuttingprocesses are milling, turning, drilling, grinding and lapping.

The emulsions according to the present invention may be employed for awide range of uses and result in better values for abrasive wear thanthose of conventional emulsions without the addition of a naturalcutting oil which is immiscible in water. They also bring about animproved protection from corrosion. In micrographs obtained using ascanning electron microscope, they appear as a “two-phase lubricant”containing a finely emulsified O/W emulsion and a coarsely dispersedcutting oil. The sizes of the actual droplets depend upon the shearingconditions and may therefore vary. The ranges of the droplet sizesoverlap, however, so that in particle size determinations by lightscattering methods, for example, using a Sympatec Helios Vectraapparatus, as a rule only one distribution maximum is obtained. This ispreferably in the range between about 0.5 and about 8 μm, in particularbetween about 1 and about 4 μm. The particle size can also be determinedby means of a light microscope or a video microscope.

The ready-to-use cooling lubricant emulsion mixed with water is thuscharacterised in that it is an oil-in-water emulsion wherein more than95% of the oil particles are smaller than 0.5 μm and into which thecutting oil which is immiscible in water is dispersed to such a degreethat it is present to the extent of at least 50% in the form ofparticles having sizes within the range of 0.5 to 8 μm.

EXAMPLES

For tests of suitability, the concentrates 1 and 3 specified above wereused as water-miscible concentrates according to step (a). The parts, byweight, of concentrate given in the Table below were stirred by means ofa glass rod into the number of parts, by weight, of water (having awater hardness corresponding to 20° Deutsche Härte [= German hardness])appropriate to produce 100 parts, by weight, of a conventional coolinglubricant emulsion. The comparison experiments 1a and 1b and also 3a and3b were carried out using these emulsions.

Cooling lubricant emulsions according to the present invention wereobtained by emulsifying 2 parts, by weight, of a natural ester-basedcutting oil in the emulsion as in 1a, and 1 part, by weight, of anatural ester-based cutting oil in the emulsion 3a. The cutting oilconsisted of a mixture of oxidation-stabilised fatty acid glycerides inthe form of triesters containing three fatty acids having 14 to 22carbon atoms per fatty acid molecule and oxidation-stabilised diesterscontaining two fatty acids having 12 to 22 carbon atoms per fatty acidmolecule (“P3 Multan® 201”, Henkel KGgA, Düsseldorf). To this end, thecutting oil was added to the emulsion mixed with water and dispersed bymeans of an Ultraturrax for 1 minute at 20,000 revolutions per minute.

A test of abrasive wear by Reichert's method was carried out as a testof suitability. This method is used for the determination of thecapacity to absorb pressure (EP behavior) and for the determination ofthe adhesive strength of liquid lubricants. Here a test roll isaccommodated by means of a system of levers on a circulating slip ring,the lower third part whereof dips into the lubricant being tested.Before the beginning of the test the test roll, which has been cleanedin special boiling-point spirit, is introduced into the rotatableholding device. The holding device is rotated into position and clamped.The slip ring remains clamped in the device for several tests, where itis again cleaned with special boiling-point spirit after each test. Thetest roll is brought onto the slip ring by slow application of theloading weight (1.5 kg). The counter positioned on the Reichert balanceis set to 0. The motor is switched on and this causes the rotating slipring, which is immersed in the lubricant, to supply the point of contactcontinuously with lubricant. When the number 100 on the counter has beenreached (100 metres friction distance) the test roll is removed from theslip ring. The test roll is disassembled and the abrasion marks whichhave formed are measured by means of a measuring microscope. Theelliptical surface is calculated from the relation 0.785*length*breadth,or is read off from a numerical table. The tests are carried outrepeatedly until the elliptical surfaces from the final three testsdiffer from one another by not more than 10%. The capacity to absorbpressure is the greater, the smaller the elliptical surface determined.

Results Parts, by Parts, by weight weight Abrasive Test emulsionConcentrate Cutting Oil wear 1a (comparison) 5 — 33 m² 1b (comparison) 7— 30 mm² 1c (according to the 5 2 18 mm² present invention) 3a(comparison) 3 — 31 mm² 3b (comparison) 5 — 30 mm² 3c (according to 3 115 mm² the present invention)

What is claimed is:
 1. A process for preparing a cooling lubricantemulsion useful for the cutting of metals comprising the steps of: (a)forming a mixture comprising an oil component, water and an emulsifier,wherein the oil component is emulsified in the water to form a mixturewhich is an oil-in-water emulsion and in which mixture more than about95 percent of oil particles have sizes that are smaller than about 0.5μm; and (b) dispersing by means of high shear in said mixture, fromabout 1 to about 14 parts by weight of a natural, water-immisciblecutting oil per 100 parts by weight of said mixture such that at least50 percent by weight of said cutting oil is in the form of particleshaving sizes within the range of about 0.5 to about 8 μm to form saidcooling lubricant emulsion.
 2. The process of claim 1 wherein themixture in step (a) is formed by mixing 2 to 15 parts by weight of awater-miscible lubricant emulsion concentrate with 85 to 98 parts byweight of water to form 100 parts by weight of said mixture.
 3. Theprocess of claim 1 wherein the weight ratio of the oil component of themixture formed in step (a) and the cutting oil is from 10:1 to 10:8. 4.The process of claim 2 wherein the cooling lubricant emulsionconcentrate comprises 20 to 60 percent by weight of said oil componentand 0 to 25 percent water.
 5. The process of claim 1 wherein the oilcomponent of the mixture formed in step (a) comprises an aliphatic ornaphthenic mineral oil, an ester lubricant, a polyolefin, or an acetalor a dialkyl ether.
 6. The process of claim 1 wherein the cutting oilcomprises one or more ester-based oils selected from the groupconsisting of natural triglycerides or products thereof, waxy esters,fatty acid esters of monoalcohols having 4 to 12 carbon atoms, and fattyacid esters of polyols.
 7. The process of claim 1 wherein the cuttingoil comprises an oxidation-stabilized fatty acid glyceride in the formof a triester containing three fatty acids having 14 to 22 carbon atomsper fatty acid molecule or an oxidation-stabilized diester containingtwo fatty acids having 12 to 22 carbon atoms per fatty acid molecule. 8.The process of claim 1 wherein the cutting oil is dispersed into themixture after said mixture has been put into use.
 9. A cooling lubricantemulsion for the cutting of metals comprising: (a) a mixture comprisingan oil component, water and an emulsifier wherein the oil component isemulsified in the water; and (b) 1 to 14 parts by weight of a natural,water-immiscible cutting oil dispersed in 100 parts by weight of saidmixture, wherein at least 50% of the cutting oil is present in the formof particles having diameters of 0.5 to 8 micrometers.
 10. The coolinglubricant emulsion of claim 9 wherein the weight ratio of the oilcomponent and the cutting oil is from 10:1 to 10:8.
 11. The coolinglubricant emulsion of claim 10 wherein the weight ratio of the oilcomponent and the cutting oil is from 10:2 to 10:7.
 12. The coolinglubricant emulsion of claim 10 wherein the oil component comprises analiphatic or naphthenic mineral oil, an ester lubricant, a polyolefin,an acetal or a dialkyl ether.
 13. The cooling lubricant emulsion ofclaim 9 wherein the cutting oil is an ester-based oil selected from thegroup consisting of natural triglycerides or products thereof, waxyesters, fatty acid esters of monoalcohols having 4 to 12 carbon atoms,and fatty acid esters of polyols.
 14. The cooling lubricant emulsion ofclaim 12 wherein the cutting oil comprises an oxidation-stabilized fattyacid glyceride in the form of a triester containing three fatty acidshaving 14 to 22 carbon atoms per fatty acid molecule or anoxidation-stabilized diester containing two fatty acids having 12 to 22carbon atoms per fatty acid molecule.
 15. A method of cutting a metalsurface comprising the steps of applying the cooling lubricant emulsionof claim 9 to said metal surface and cutting said metal surface.